JPH0797233A - Fiber optic line citation heating furnace - Google Patents

Abstract

(57) [Abstract] [Purpose] In drawing an optical fiber preform, it is angularly heated uniformly to obtain an optical fiber having a perfect circular cross section. [Structure] An approximately hollow columnar shape coaxially arranged on the outer side of an optical fiber preform 1 to be spun, and electrodes are attached to respective circumferential positions of the lower end in the axial direction which are angularly 180 degrees apart and face each other. In the optical fiber line drawing heating furnace having the carbon heater 2, the lower end of the carbon heater 2 extends to the vicinity of a point P at which the molten glass wire drawn from the optical fiber preform 1 becomes sufficiently thin. As another configuration, the carbon heater 2 is reciprocally rotated by 90 degrees around the optical fiber preform 1 to cancel angular uneven heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber line drawing heating furnace.

[0002]

2. Description of the Related Art FIG. 3 is a schematic diagram for explaining an optical fiber drawing process. The optical fiber preform 1 supported by the feed screw shaft 103 so as to be vertically feedable is heated and melted by a heating furnace including a hollow cylindrical carbon heater 102 coaxially arranged around the lower portion thereof. It is drawn from the lower end. Reference numeral 10 in the figure
4 is a coating device, 105 is a take-up machine, and 106 is a take-up machine.

[0003]

Considering FIG. 4, which is an enlarged view of the portion of the heating furnace, the carbon heater 10 will be described.
Reference numeral 2 denotes a hollow cylindrical shape, but the temperature distribution inside thereof is exactly angularly uniform, that is, the isotherm at a certain cross-section position in the axial direction of the carbon heater is the carbon heater 102.
It does not become concentric with respect to the cross-sectional circle of, but the fact that the temperature is higher at the lower end of the carbon heater, to which the electrode 3 is attached, in the vicinity of opposite circumferential positions 180 degrees apart from each other, is higher than other parts. Then, the mounting direction of the electrode 3, that is, the XX line direction shown in the drawing is the minor axis, and YY is orthogonal to this.
It is known that it becomes an ellipse whose major axis is the line direction.

As a result, the outer peripheral surface of the optical fiber preform 1 to be heated and melted is not exactly concentric with the carbon heater 102 when viewed in the axial cross section, and is similar to the above-mentioned isotherm as shown in the drawing. Tend to be elliptical.
That is, qualitatively speaking, the side of the carbon heater 102 facing the high temperature portion becomes thin.

The non-circularization phenomenon of the melted cross section of the optical fiber preform 1 in the heated and melted state as described above causes the non-circularity of the cross-sectional shape of the optical fiber drawn from here, which hinders the production of high-quality optical fibers. Is a serious drawback.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve this problem, and the means of the invention according to claim 1 to solve the problem is to provide an optical fiber preform to be spun. Wire-line heating of an optical fiber having a substantially hollow cylindrical shape coaxially arranged on the outside and having carbon heaters attached to respective circumferential positions of the lower end in the axial direction facing each other 180 degrees apart. In the furnace, the lower end of the carbon heater extends to a point near a point where a molten glass wire drawn from the optical fiber preform becomes sufficiently thin, and a line-referring heating furnace for an optical fiber.

The means of the invention of claim 2 is a substantially hollow cylindrical shape coaxially arranged on the outer side of the optical fiber preform to be spun, and the lower end portion in the axial direction is angularly separated by 180 degrees. In an optical fiber line citation heating furnace having carbon heaters with electrodes attached at opposing circumferential positions, the carbon heaters have about 9 axes around their central axis.
The optical fiber wire-drawing heating furnace is characterized in that it can be reciprocally rotated by 0 degrees.

[0008]

[Function] Since the lower end of the carbon heater to which the electrode is attached extends to the vicinity of the point where the molten glass wire drawn from the optical fiber preform becomes sufficiently thin, the main body of the optical fiber preform has a temperature distribution. The heater becomes uneven and is surrounded by the center of the heater, and is heated uniformly.

Since the carbon heater is angularly reciprocally rotated by 90 degrees, the elliptical temperature inside the heater is offset and equalized in the long and short axis directions, and the optical fiber preform is uniformly heated. .

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. Reference numeral 2 is a hollow cylindrical carbon heater, and electrodes 3 are attached to the peripheral portion of the lower end of the carbon heater at opposing positions angularly separated by 180 degrees. Reference numeral 4 indicates the flow of the coolant for cooling the electrode 3.

A feature of the present invention is that the lower end 2A of the carbon heater 2 extends to the vicinity of a point P where the molten glass wire 1A drawn from the optical fiber preform 1 and hanging down becomes sufficiently thin.

As a result of such a structure of the carbon heater 2, the main body portion of the optical fiber preform 1 is located in the central portion apart from the electrode mounting portion at the lower end of the carbon heater where the temperature distribution is not uniform. Carbon heater 2
Therefore, the cross section of the optical fiber preform can be obtained as a substantially circular cross-section by being uniformly heated angularly without being affected by the nonuniform heating.

FIG. 2 shows a second embodiment of the present invention. An outer tooth ring 6 is attached to the outer peripheral portion of the carbon heater 5 arranged around the optical fiber preform 1 via an appropriate heat insulating member 51, and a rack 8 meshing with the outer tooth ring 6 is biased to the rotating disk 10. It is configured to be reciprocally moved by a link rod 9 that is intentionally connected. The stroke of the rack 8 is selected so that the rotation angle of the outer tooth ring 6 is 90 degrees.

A suitable movable electrode 7 is attached as an electrode, the link rod 9 is connected in the middle by a suitable heat insulating member 91 having a low thermal conductivity, and the rotating disk 10 is constantly cooled by a cooling device 11. Of course, it takes an adiabatic structure.

[0015]

According to the present invention, since the lower end of the carbon heater to which the electrode is attached extends to near the point where the molten glass wire drawn from the optical fiber preform becomes sufficiently thin, the optical fiber preform The main body part of the heater is heated from the vicinity of the lower end of the heater where the temperature distribution becomes uneven and is surrounded by the center of the heater. As a result, it is heated uniformly and the cross section of the optical fiber preform is almost a perfect circle. Is effective.

Also, since the carbon heater is angularly reciprocally rotated by 90 degrees, the elliptical temperature inside the heater is offset and equalized in the long and short axis directions, and the optical fiber preform is uniformly heated. It is extremely effective to make the cross section of the optical fiber preform almost circular.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a first embodiment device of the present invention.

FIG. 2 is a plan view showing a partial cross-sectional view of a second embodiment device of the present invention.

FIG. 3 is a simplified side view for explaining a heating furnace for drawing an optical fiber preform.

FIG. 4 is a side sectional view and a transverse sectional view showing a conventional heating furnace for wire drawing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber base material 2,5 Carbon heater 3 Electrode 4 Coolant flow 51,91 Thermal insulation member 6 External tooth ring 7 Movable electrode 8 Rack 9 Link rod 10 Rotating disk 11 Cooling device

Claims (2)

[Claims] 1. A substantially hollow cylindrical column coaxially arranged on the outer side of an optical fiber preform (1) to be spun, at a circumferential position where the lower end in the axial direction is angularly 180 degrees apart and faces each other. In a fiber optic line citation heating furnace having carbon heaters (2) each having an electrode attached, a molten glass wire drawn from the optical fiber preform (1) is sufficiently thin at the lower end of the carbon heater (2). A line citation heating furnace for optical fibers, characterized in that it extends to the vicinity of the point (P). 2. A substantially hollow cylindrical column coaxially arranged on the outer side of an optical fiber preform (1) to be spun, and at the circumferential positions facing each other at an angle of 180 degrees at the lower end in the axial direction. An optical fiber wire-drawing heating furnace having carbon heaters (2) each having an electrode attached, characterized in that the carbon heaters (2) are configured to be capable of reciprocating about 90 degrees about their central axes. Optical fiber line citation heating furnace.